1. Field of the Invention
This invention relates to a magnetic head in which a magnetic gap is formed by a portion of a ferrite core confronting the gap or a magnetic core having MIG (Metal in Gap) structure in which a metal magnetic film is formed at a portion of a ferrite core confronting the gap, and especially relates to a magnetic head being able to suppress noise fluctuation in a high frequency band.
2. Description of the Related Art
FIG. 11 is a perspective view of the conventional magnetic head while FIG. 12 is an enlarged plane view of a magnetic head viewed from the rubbing surface side of a recording medium.
The reference numeral 1 in FIG. 11 is a core made of a single crystal ferrite comprising Fe.sub.2 O.sub.3, MnO and ZnO or a joined material of the single crystal ferrite with a polycrystalline ferrite. The core 1, 1 is provided with a confronting portion 1a, 1a and an inclined face (track width regulating face) 1b, 1b inclined against the confronting portion 1a, 1a.
A metal magnetic film 2 having a high saturation magnetic flux density such as Fe-Ta-N alloy or Fe-Al-Si alloy (sendust) is coated on the confronting portion 1a 1a and inclined face (track width regulating face) 1b, 1b, wherein the metal magnetic films coated on the confronting portion 1a, 1a are joined with each other via a non-magnetic material to form a magnetic gap G with the junction part. Tw denotes track width.
The reference numeral 3 is an adhering glass to join the metal magnetic film 2, 2 coated on the confronting portion 1a, 1a and the adhering glass 3 is also filled on the surface of the metal magnetic film 2 coated on the core on the inclined face (track width regulating face) 1b, 1b. The reference numeral 4 is a recording/reproducing coil. While the azimuthal angle of the magnetic gap is made 0.degree. in FIG. 12, the practical magnetic head has an azimuthal angle so as to turn the magnetic gap clockwise or counter clockwise against the magnetic circuit direction.
It is generally recognized that the magnetic anisotropy along the crystallographic axis in the single crystal ferrite is determined by the magnetocrystalline anisotropic energy K1 that depends on the composition of the single crystal ferrite. However, the magnetic anisotropy of the magnetic head as shown in FIG. 11 is not only determined by the magnetocrystalline anisotropic energy K1 but also depends on the apparent magnetic anisotropic energy Ea obtained by subtracting the magnetoelastic energy that is proportional to the product of stress .sigma..sub.total times saturation magnetorestriction .lambda.s from the magnetocrystalline anisotropic energy K1.
Apparent magnetic anisotropic energy; Ea=(Magnetocrystalline anisotropic energy; K1)-(Magnetoelastic energy; 3/2.multidot..lambda.s.multidot..sigma..sub.total)
Magnetic anisotropy will be strengthened when the absolute value of Ea becomes large while the former will be weak when the latter is small.
Ea was usually made as small as possible to enhance the magnetic permeability .mu. that is inversely proportional to Ea as high as possible in the conventional magnetic heads. Accordingly, the absolute value of the magnetoelastic energy was reduced by making the absolute value of the magnetocrystalline anisotropic energy K1 as well as the absolute values of the saturation magnetorestriction .lambda.s and stress .sigma..sub.total small for the purpose of diminishing Ea described above.
The magnetocrystalline anisotropic energy K1 and saturation magnetorestriction .lambda.s are mainly determined by the content of Fe.sub.2 O.sub.3 in the ferrite. On the other hand, the mean thermal expansion coefficient .alpha..sub.ferrite of the single crystal ferrite is largely dependent on the Zn content, thereby the absolute value of stress .sigma..sub.total can be reduced by making the difference between the mean thermal expansion coefficient .alpha..sub.metal of the soft magnetic material forming the metal magnetic film 2 and the mean thermal expansion coefficient .alpha..sub.ferrite of the single crystal ferrite small. The mean thermal expansion coefficient .alpha..sub.metal of sendust that is used for the conventional metal magnetic film 2 is about 115 (10.sup.-7 /.degree. C.)
FIG. 3 is a three components phase diagram of a single crystal ferrite comprising Fe.sub.2 O.sub.3 MnO and ZnO. The composition ratio of the single crystal ferrite by which the absolute values of the magnetocrystalline anisotropic energy K1, saturation magnetorestriction .lambda.s and stress .sigma..sub.total are made small is represented by (a) in the figure where the ratio of (Fe.sub.2 O.sub.3 :MnO:ZnO)=(53 to 55 mol % 26 to 31 mol %:16 to 19 mol %). Cores 1, 1 of the conventional magnetic head were formed by single crystal ferrites with a composition within the area of (a).
However, when a magnetic head in which the absolute values of the magnetocrystalline anisotropic energy K1 and magnetoelastic energy are made small to diminish the apparent magnetic anisotropic energy Ea was used for recording/reproduction at a high frequency for DDS (Digital Data Storage), it was confirmed that noise fluctuations at frequencies other than the frequency of the carrier signal became large and C/N ratio (the ratio between the carrier recording level and noise level) was deteriorated, thereby the error rate was increased.
The reason why the noise fluctuation is enlarged is supposed as follows: The magnetized state in the core, in which the absolute value of the magnetic anisotropy energy Ea is diminished, is made to be readily fluctuated by the influence of the exciting current during recording, so that the magnetic energy in the ferrite becomes unstable in the demagnetization time when the polarity of the alternating magnetic field imparted to the core is instantaneously quenched and thereby the magnetic polarity in the vicinity of the gap at the moment of demagnetization becomes unstable. This probably means that the polarity of the apparent magnetic anisotropy energy Ea is so susceptible to the exciting current for recording.